1. Field of the Invention
This invention relates to the field of computer systems with display devices. Specifically, the field is that of interactive computer display control devices used for drawing and manipulating graphic or textual images on a display screen.
2. Prior Art
Interactive computer systems are commonly used for computer-aided design and drafting. These computer applications typically provide interactive controls for creating and manipulating graphic and textual images on a computer display screen. For example, a user operating one of these applications may be able to select from a plurality of drawing tools provided by the application. These drawing tools typically include controls for drawing images such as rectangles, polygons, circles, or blocks of text. A user may select a particular tool and position the associated image in a window on the display screen using a cursor control device, such as a mouse or a trackball. One such interactive computer display system is Claris CAD, developed jointly by Claris Incorporated, Santa Clara, Calif., and Craig S. Young d/b/a Computer Aided Systems for Engineering, Zephyr Cove, Nev.
A number of disadvantages exist with the image control mechanisms existing in the prior art. Some prior art computer assisted drawing mechanisms do not include a capability for associating dimensions between two images. This can be particularly troublesome when the two images are actually depictions of the same object as seen in different views. In this situation, the dimension of the sides or areas of one image correspond to the sides and areas of the other image. Thus, it is necessary that the dimensions of each image be accurately depicted. Since these prior art systems treat the images as independent entities, this accurate depiction is difficult to achieve. Moreover, a projection of points from one object onto another object is difficult to achieve in these prior art systems.
Another disadvantage of prior art computer-assisted design and drafting systems becomes apparent when images on the computer display screen are joined, overlaid, or extended. For example, a typical operation in a computer-assisted drafting application may be to draw two separate rectangular images. Part of one of these rectangles may overlay a portion of the other rectangle. The overlay portion may be represented in a number of ways. Typically, prior art computer-assisted drawing systems display overlaid images depending upon which image was created last. The most recently created image is usually displayed on the top layer. Thus, the edges of the top layered image are visible while portions of the edges of the overlaid image are hidden. Prior art systems provide little support for manipulating these overlaid and overlaying regions. Accordingly, there exists a need to provide an efficient, yet simple user interface for creating and manipulating a plurality of graphic images on a computer display screen.
As will be discussed below, the present invention provides an improved computer-assisted design and drawing system which overcomes the disadvantages of the prior art systems.